He was accused of "spoofing" the Chicago Mercantile Exchange's futures market — which means making a large bet, waiting for the market to react to it, and then canceling the trade and betting against other traders' reactions.

Prosecutors say Sarao sparked a sudden market crash on May 6, 2010 in this way.

Sarao, 37, reportedly traded futures from his parents' basement in the suburbs of London.

According to the complaint, he allegedly used an algorithm to manipulate the market for E-Mini S&P 500 futures contracts, or "E-Minis," on the CME.

"Sarao's alleged manipulation earned him significant profits and contributed to a major drop in the U.S. stock market on May 6, 2010, that came to be known as the 'Flash Crash,'" the Department of Justice said in a statement. "On that date, the Dow Jones Industrial Average fell by approximately 600 points in a five-minute span, following a drop in the price of E-Minis."

He was arrested and charged with one count of wire fraud, 10 counts of commodities fraud, 10 counts of commodities manipulation, and one count of spoofing.

Sarao faces up to 30 years in prison, according to Bloomberg, though it's unlikely he will receive a sentence that severe. He spent four months in prison last year before securing bail.

The case is U.S. v. Sarao, 15-cr-00075, U.S. District Court, Northern District of Illinois (Chicago).